Isomerization Catalyst and Process

ABSTRACT

A catalyst and process is disclosed to selectively upgrade a paraffinic feedstock to obtain an isoparaffin-rich product for blending into gasoline. The catalyst comprises a support of a tungstated oxide or hydroxide of a Group IVB (IUPAC 4) metal, a phosphorus component, and at least one platinum-group metal component which is preferably platinum. The catalyst has a structure other than a hetropoly anion structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Division of copending application Ser. No.11/304,521, filed Dec. 15, 2005, which in turn is a Continuation-In-Partof application Ser. No. 10/869,252, filed Jun. 16, 2004, now abandoned,which in turn is a Division of application Ser. No. 10/243,524 filedSep. 13, 2002, now abandoned, the contents of which are herebyincorporated by reference in their entirety.

FIELD OF THE INVENTION

This invention relates to an improved catalytic composite and processfor the conversion of hydrocarbons, and more specifically for theselective upgrading of a paraffinic feedstock by isomerization.

BACKGROUND OF THE INVENTION

The widespread removal of lead antiknock additive from gasoline and therising fuel-quality demands of high-performance internal-combustionengines have compelled petroleum refiners to install new and modifiedprocesses for increased “octane,” or knock resistance, in the gasolinepool. Refiners have relied on a variety of options to upgrade thegasoline pool, including higher-severity catalytic reforming, higher FCC(fluid catalytic cracking) gasoline octane, isomerization of lightnaphtha and the use of oxygenated compounds. Such key options asincreased reforming severity and higher FCC gasoline octane result in ahigher aromatics content of the gasoline pool at the expense oflow-octane heavy paraffins.

Refiners are also faced with supplying reformulated gasoline to meettightened automotive emission standards. Reformulated gasoline differsfrom the traditional product in having a lower vapor pressure, lowerfinal boiling point, increased content of oxygenates, and lower contentof olefins, benzene and aromatics. Benzene content generally is beingrestricted to 1% or lower, and is limited to 0.8% in U.S. reformulatedgasoline. Gasoline aromatics content is likely to be lowered,particularly as distillation end points (usually characterized as the90% distillation temperature) are lowered, since the high-boilingportion of the gasoline which thereby would be eliminated usually is anaromatics concentrate. Since aromatics have been the principal source ofincreased gasoline octanes during the recent lead-reduction program,severe restriction of the benzene/aromatics content and high-boilingportion will present refiners with processing problems. These problemshave been addressed through such technology as isomerization of lightnaphtha to increase its octane number, isomerization of butanes asalkylation feedstock, and generation of additional light olefins asfeedstock for alkylation and production of oxygenates using FCC anddehydrogenation. This issue often has been addressed by raising the cutpoint between light and heavy naphtha, increasing the relative quantityof naphtha to an isomerization unit.

Additionally, instead of reforming, the isomerization of longer chainhydrocarbons such as C₇ and C₈ hydrocarbons into branched hydrocarbonsof higher octane could be used to increase the octane number of fuelswithout increasing the amount of aromatics. However, many isomerizationcatalysts suffer significant disadvantages when applied to the longerchain hydrocarbons. A principal problem is the generation of byproductssuch as cracked hydrocarbon materials. The cracking decreases the amountof long chain paraffins available for isomerization and reduces theultimate yield.

Several catalysts for isomerization are known, and a family oftungstated zirconia catalysts have been used. For example, U.S. Pat. No.5,510,309 B1, U.S. Pat. No. 5,780,382 B1, U.S. Pat. No. 5,854,170, andU.S. Pat. No. 6,124,232 B1 teach methods of making an acidic solidhaving a Group IVB (IUPAC 4) metal oxide modified with an oxyanion of aGroup VIB (IUPAC 6) metal such as zirconia modified with tungstate. U.S.Pat. No. 6,184,430 B1 teaches a method of cracking a feedstock bycontacting the feedstock with a metal-promoted anion modified metaloxide catalyst where the metal oxide is one or more of ZrO₂, HfO₂, TiO₂and SnO₂, the modifier is one or more of SO₄ and WO₃, and the metal isone or more of Pt, Ni, Pd, Rh, Ir, Ru, Mn, and Fe.

Others have added a noble metal such as platinum to the tungstatedzirconia catalysts above, see U.S. Pat. No. 5,719,097; U.S. Pat. No.6,080,904 B1; and U.S. Pat. No. 6,118,036 B1. A catalyst having an oxideof a Group IVB (IUPAC 4) metal modified with an anion or oxyanion of aGroup VIB (IUPAC 6) metal and a Group IB (IUPAC 11) metal or metal oxideis disclosed in U.S. Pat. No. 5,902,767. In U.S. Pat. No. 5,648,589 andU.S. Pat. No. 5,422,327, a catalyst having a Group VIII (IUPAC 8, 9, and10) metal and a zirconia support impregnated with silica and tungstenoxide and a process of isomerization using the catalyst is disclosed. Aprocess for forming a diesel fuel blending component uses an componentuses an acidic solid catalyst having a Group IVB (IUPAC 4) metal oxidemodified with an oxyanion of Group VIB (IUPAC 6) metal and iron ormanganese in U.S. Pat. No. 5,780,703 B1. U.S. Pat. No. 5,310,868 andU.S. Pat. No. 5,214,017 teach catalyst compositions containing sulfatedand calcined mixtures of (1) a support containing an oxide or hydroxideof IUPAC 4 (Ti, Zr, Hf), (2) an oxide or hydroxide of IUPAC 6 (Cr, Mo,W); IUPAC 7 (Mn, Tc, Re), or IUPAC 8, 9, and 10 (Group VIII) metal, (3)an oxide or hydroxide of IUPAC 11 (Cu, Ag, Au), IUPAC 12 (Zn, Cd, Hg),IUPAC 3 (Sc, Y), IUPAC 13 (B, Al, Ga, In, Tl), IUPAC 14 (Ge, Sn, Pb),IUPAC 5 (V, Nb, Ta), or IUPAC 6 (Cr, Mo, W), and (4) a metal of thelanthanide series. U.S. Pat. No. 5,489,733 teaches a catalyst having azirconium hydroxide support, a Group VIII metal, and a heteropolyacidselected from the group consisting of the exchanged aluminum salt of12-tungstophosphoric acid, the exchanged salt of 12-tungstosilicic acid,and mixtures thereof. The catalyst is used for isomerization processeshaving a feed comprising C_(n) or C_(n)+ wherein n=4.

Applicant has developed a more effective catalyst that has proved to besurprisingly superior to those already known for the isomerization ofhydrocarbons and especially C₇ and C₈ hydrocarbons.

SUMMARY OF THE INVENTION

A purpose of the present invention is to provide an improved catalystand process for hydrocarbon conversion reactions. Another purpose of thepresent invention is to provide improved technology to upgrade naphthato gasoline. A more specific purpose is to provide an improved catalystand process for the isomerization of full boiling point range naphtha toobtain a high-octane gasoline component. This invention is based on thediscovery that a catalyst containing a phosphorous compound such as aphosphorous oxide, a phosphorous hydroxide, a phosphorous halide, aphosphorous oxyhalide, a phosphorous carbonate, a phosphorous nitrate, aphosphorous sulfate, or a phosphorus component present within thesupport plus a platinum-group component provides superior performanceand stability in the isomerization of full boiling point range naphthato increase its isoparaffin content. The catalyst has a structure otherthan a heteropoly anion structure.

A broad embodiment of the present invention is directed to a catalystcomprising a tungstated support of an oxide or hydroxide of a Group IVB(IUPAC 4) metal, preferably zirconium oxide or hydroxide, at least afirst component which is a phosphorus component, and at least a secondcomponent being a platinum-group metal component. The second componentpreferably consists of a single platinum-group metal, which is mostpreferably a platinum component. The catalyst optionally contains aninorganic-oxide binder, especially alumina. The catalyst has a structureother than a heteropoly anion structure.

An additional embodiment of the invention is a method of preparing thecatalyst of the invention by tungstating the Group IVB (IUPAC 4) metaloxide or hydroxide, incorporating a first component which is aphosphorous component, and the second component which is aplatinum-group metal, and preferably binding the catalyst with arefractory inorganic oxide. The catalyst has a structure other than aheteropoly anion structure.

In another aspect, the invention comprises converting hydrocarbons usingthe catalyst of the invention. In yet another embodiment, the inventioncomprises the isomerization of isomerizable hydrocarbons using thecatalyst of the invention. The hydrocarbons preferably comprise a fullboiling point range naphtha which is isomerized to increase itsisoparaffin content and octane number as a gasoline blending stock.

These as well as other embodiments will become apparent from thedetailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of the conversion of n-heptane achieved by selectedcatalysts made in Example 1.

FIG. 2 is a plot of the selectivities of the catalysts of FIG. 1 forn-heptane isomerization.

FIG. 3 is a plot of the selectivities of the catalysts of FIG. 1 for theisomerization of n-heptane to 2,2-dimethylpentane and2,4-dimethylpentane.

FIG. 4 is a plot of the yields of the catalysts of FIG. 1 for theisomerization of n-heptane to 2,2-dimethylpentane and2,4-dimethylpentane.

FIG. 5 is a plot of the conversion of n-heptane achieved by selectedcatalysts made in Example 1 where silicon is a modifier.

FIG. 6 is a plot of the selectivities of the catalysts of FIG. 5 forn-heptane isomerization.

FIG. 7 is a plot of the selectivities of the catalysts of FIG. 5 for theisomerization of n-heptane to 2,2-dimethylpentane and2,4-dimethylpentane.

FIG. 8 is a plot of the yields of the catalysts of FIG. 5 for theisomerization of n-heptane to 2,2-dimethylpentane and2,4-dimethylpentane.

FIG. 9 is a set of three X-ray powder diffraction patterns correspondingto catalysts of Table 2.

FIG. 10 is a set of four X-ray powder diffraction patterns correspondingto catalysts of Table 2.

DETAILED DESCRIPTION OF THE INVENTION

The support material of the catalyst of the present invention comprisesan oxide or hydroxide of a Group IVB (IUPAC 4) metal, see Cotton andWilkinson, Advanced Inorganic Chemistry, John Wiley & Sons (FifthEdition, 1988) and including zirconium, titanium and hafnium.Preferably, the metal is selected from zirconium and titanium, withzirconium being especially preferred. The preferred zirconium oxide orhydroxide is converted via calcination to crystalline form. Tungstate iscomposited on the support material to form, it is believed without solimiting the invention, a mixture of Brönsted and Lewis acid sites. Acomponent of at least one Group IVA (IUPAC 14) component, Group VA(IUPAC 15) component, or mixtures thereof, is incorporated into thecomposite by any suitable means. A platinum-group metal component isadded to the catalytic composite by any means known in the art to effectthe catalyst of the invention, e.g., by impregnation. Optionally, thecatalyst is bound with a refractory inorganic oxide. The support,tungstate, metal components, and optional binder may be composited inany order effective to prepare a catalyst useful for the conversion ofhydrocarbons, and particularly the isomerization of hydrocarbons.

Production of the support of the present catalyst may be based on ahydroxide of a Group IVB (IUPAC 4) metal as raw material. For example,suitable zirconium hydroxide is available from MEI of Flemington, N.J.Alternatively, the hydroxide may be prepared by hydrolyzing metaloxy-anion compounds, for example ZrOCl₂, ZrO(NO₃)₂, ZrO(OH)NO₃, ZrOSO₄,TiOCl₂ and the like. Note that commercial ZrO(OH)₂ contains asignificant amount of Hf, about 1 weight percent. Zirconium alkoxidessuch as zirconyl acetate and zirconium propoxide may be used as well.The hydrolysis can be effected using a hydrolyzing agent such asammonium hydroxide, sodium hydroxide, potassium hydroxide, sodiumsulfate, (NH₄)₂HPO₄ and other such compounds known in the art. The metaloxy-anion component may in turn be prepared from available materials,for example, by treating ZrOCO₃ with nitric acid. The hydroxide aspurchased or generated by hydrolysis preferably is dried at atemperature of from about 100° C. to 300° C. to vaporize volatilecompounds.

A tungstated support is prepared by treatment with a suitabletungstating agent to form a solid strong acid. Liquid acids whosestrength is greater than sulfuric acid have been termed “superacids”. Anumber of liquid superacids are known in the literature includingsubstituted protic acids, e.g., trifluoromethyl substituted H₂SO₄,triflic acid and protic acids activated by Lewis acids (HF plus BF₃).While determination of the acid strength of liquid superacids isrelatively straightforward, the exact acid strength of a solid strongacid is difficult to directly measure with any precision because of theless defined nature of the surface state of solids relative to the fullysolvated molecules found in liquids. Accordingly, there is no generallyapplicable correlation between liquid superacids and solid strong acidssuch that if a liquid super acid is found to catalyze a reaction, thereis no corresponding solid strong acid which one can automatically chooseto carry out the same reaction. Therefore, as will be used in thisspecification, “solid strong acids” are those that have an acid strengthgreater than sulfonic acid resins such as Amberlyst®-15. Additionally,since there is disagreement in the literature whether some of thesesolid acids are “superacids” only the term solid strong acid as definedabove will be used herein. Another way to define a solid strong acid isa solid comprising of interacting protic and Lewis acid sites. Thus,solid strong acids can be a combination of a Bronsted (protonic) acidand a Lewis acid component. In other cases, the Bronsted and Lewis acidcomponents are not readily identified or present as distinct species,yet they meet the above criteria.

Tungstate ions are incorporated into a catalytic composite, for example,by treatment with ammonium metatungstate in a concentration usually ofabout 0.1 to 20 mass percent tungsten and preferably from about 1 to 15mass percent tungsten. Compounds such as metatungstic acid, sodiumtungstate, ammonium tungstate, ammonium paratungstate, which are capableof forming tungstate ions upon calcining, may be employed as alternativesources. Preferably, ammonium metatungstate is employed to providetungstate ions and form a solid strong acid catalyst. The tungstatecontent of the finished catalyst generally is in the range of about 0.5to 30 mass-%, and preferably is from about 1 to 25 mass-% on anelemental basis. The tungstate composite is dried, preferably followedby calcination at a temperature of about 450° C. to 1000° C.particularly if the tungstanation is to be followed by incorporation ofthe platinum-group metal.

A first component, comprising one or more of the Group IVA (IUPAC 14)components, Group VA (IUPAC 15) components, or mixtures thereof, isanother essential component of the present catalyst. Included in theGroup IVA components are silicon, germanium, tin, and lead. Included inthe Group VA components are nitrogen, phosphorus, arsenic, antimony, andbismuth. Preferred elements include silicon, phosphorus, and germanium,with silicon being the most preferred. The first component may, ingeneral, be present in the catalytic composite in any catalyticallyavailable form such as the elemental metal, a compound such as theoxide, hydroxide, halide, oxyhalide, carbonate or nitrate. The firstcomponent is preferably an oxide, an intermetallic with platinum, asulfate, or in the zirconia lattice. The materials are generallycalcined between 450° C. and 1000° C., with a preferred temperature ofabove 600° C. and at about 800° C., and thus in the oxide form. Althoughit is not intended to so restrict the present invention, it is believedthat best results are obtained when the first component is present inthe composite in a form wherein substantially all of the first componentis in an oxidation state above that of the elemental state such as inthe form of the oxide, oxyhalide or halide or in a mixture thereof andthe subsequently described oxidation and reduction steps that arepreferably used in the preparation of the instant catalytic compositeare specifically designed to achieve this end. The first component canbe incorporated into the catalyst in any amount which is catalyticallyeffective, suitably from about 0.01 to about 10 mass-% first componentin the finished catalyst on an elemental basis. Best results usually areachieved with about 1 to about 5 mass-% of the first component,calculated on an elemental basis.

The first component is incorporated in the catalytic composite in anysuitable manner known to the art, such as by coprecipitation,coextrusion with the porous carrier material, or impregnation of theporous carrier material either before, after, or simultaneously withtungstate though not necessarily with equivalent results. For ease ofoperation, it is preferred to simultaneously incorporate the firstcomponent with the tungstate, however, the first component and thetungstate are each individual materials. It is most preferred toincorporate the incorporate the platinum-group metal component last. Asto the first component and the platinum-group metal, the order ofaddition between the two does not have a significant impact.

One method of depositing the first component involves impregnating thesupport with a solution (preferably aqueous) of a decomposable compoundof the first component. By decomposable is meant that upon heating, thecompound is converted to element or oxide with the release ofbyproducts. Illustrative of the decomposable compounds withoutlimitation are complexes or compounds such as, nitrates, halides,sulfates, acetates, organic alkyls, hydroxides, and the like compounds.Conditions for decomposition include temperatures ranging from about200° C. to about 400° C. The first component can be impregnated onto thecarrier either prior to, simultaneously with, or after theplatinum-group metal component, although not necessarily with equivalentresults. If a sequential technique is used, the composite can be driedor dried and calcined in between impregnations.

A second component, a platinum-group metal, is an essential ingredientof the catalyst. The second component comprises at least one ofplatinum, palladium, ruthenium, rhodium, iridium, or osmium; platinum ispreferred, and it is especially preferred that the platinum-group metalconsists essentially of platinum. The platinum-group metal component mayexist within the final catalytic composite as a compound such as anoxide, sulfide, halide, oxyhalide, etc., in chemical combination withone or more of the other ingredients of the composite or as the metal.Amounts in the range of from about 0.01 to about 2 mass-% platinum-groupmetal component, on an elemental basis, are effective, and from about0.1 to 1 mass-% platinum-group metal component, on an elemental basis,are preferred. Best results are obtained when substantially all of theplatinum-group metal is present in the elemental state.

The second component, a platinum-group metal component, is deposited onthe composite using the same means as for the first component describedabove. Illustrative of the decomposable compounds of the platinum groupmetals are chloroplatinic acid, ammonium chloroplatinate, bromoplatinicacid, dinitrodiamino platinum, sodium tetranitroplatinate, rhodiumtrichloride, hexa-amminerhodium chloride, rhodium carbonylchloride,sodium hexanitrorhodate, chloropalladic acid, palladium chloride,palladium nitrate, diamminepalladium hydroxide, tetraamminepalladiumchloride, hexachloroiridate (IV) acid, hexachloroiridate (III) acid,ammonium hexachloroiridate (III), ammonium aquohexachloroiridate (IV),ruthenium tetrachloride, hexachlororuthenate, hexaamminerutheniumchloride, osmium trichloride and ammonium osmium chloride. The secondcomponent, a platinum-group component, is deposited on the supporteither before, after, or simultaneously with tungstate and/or the firstcomponent though not necessarily with equivalent results. It ispreferred that the platinum-group component is deposited on the supporteither after or simultaneously with tungstate and/or the firstcomponent. Again, each of the components, the tungstate, the firstcomponent, and the second component are each individual materials.

In addition to the first and second components above, the catalyst mayoptionally further include a third component of iron, cobalt, nickel,rhenium or mixtures thereof. Iron is preferred, and the iron may bepresent in amounts ranging from about 0.1 to about 5 mass-% on anelemental basis. The third component, such as iron, may function tolower the amount of the first component needed in the optimalformulation. The third component may be deposited on the composite usingthe same means as for the first and second components as describedabove. When the third component is iron, suitable compounds wouldinclude iron nitrate, iron halides, iron sulfate and any other solubleiron compound.

The catalytic composite described above can be used as a powder or canbe formed into any desired shapes such as pills, cakes, extrudates,powders, granules, spheres, etc., and they may be utilized in anyparticular size. The composite is formed into the particular shape bymeans well known in the art. In making the various shapes, it may bedesirable to mix the composite with a binder. However, it must beemphasized that the catalyst may be made and successfully used without abinder. The binder, when employed, usually comprises from about 0.1 to50 mass-%, preferably from about 5 to 20 mass-%, of the finishedcatalyst. Refractory inorganic oxide are suitable binders. Examples ofbinders without limitation are silica, aluminas, silica-alumina,magnesia, zirconium and mixtures thereof. A preferred binder material isalumina, with eta—and/or especially gamma-alumina being favored. Usuallythe composite and optional binder are mixed along with a peptizing agentsuch as HCl, HNO₃, KOH, etc. to form a homogeneous mixture which isformed into a desired shape by forming means well known in the art.These forming means include extrusion, spray drying, oil dropping,marumarizing, conical screw mixing, etc. Extrusion means include screwextruders and extrusion presses. The forming means will determine howmuch water, if any, is added to the mixture. Thus, if extrusion is used,then the mixture should be in the form of a dough, whereas if spraydrying or oil dropping is used, then enough water needs to be present inorder to form a slurry. These slurry. These particles are calcined at atemperature of about 260° C. to about 650° C. for a period of about 0.5to about 2 hours.

The catalytic composites of the present invention either as synthesizedor after calcination can be used as catalysts in hydrocarbon conversionprocesses. Calcination is required, for example, to form zirconium oxidefrom zirconium hydroxide. Hydrocarbon conversion processes are wellknown in the art and include cracking, hydrocracking, alkylation of botharomatics and isoparaffins, isomerization, polymerization, reforming,dewaxing, hydrogenation, dehydrogenation, transalkylation, dealkylation,hydration, dehydration, hydrotreating, hydrodenitrogenation,hydrodesulfurization, methanation, ring opening, and syngas shiftprocesses. Specific reaction conditions and the types of feeds, whichcan be used in these processes, are set forth in U.S. Pat. No. 4,310,440and U.S. Pat. No. 4,440,871, which are hereby incorporated by reference.A preferred hydrocarbon conversion process is the isomerization ofparaffins.

In a paraffin isomerization process, common naphtha feedstocks boilingwithin the gasoline range contain paraffins, naphthenes, and aromatics,and may comprise small amounts of olefins. Feedstocks which may beutilized include straight-run naphthas, natural gasoline, syntheticnaphthas, thermal gasoline, catalytically cracked gasoline, partiallyreformed naphthas or raffinates from extraction of aromatics. Thefeedstock essentially is encompassed by the range of a full-rangenaphtha, or within the boiling point range of 0° C. to 230° C.

The principal components of the preferred feedstock are alkanes andcycloalkanes having from 4 to 10 carbon atoms per molecule, especiallythose having from 7 to 8 carbon atoms per molecule. Smaller amounts ofaromatic and olefinic hydrocarbons also may be present. Usually, theconcentration of C₇ and heavier components is more than about 10 mass-%of the feedstock. Although there are no specific limits to the totalcontent in the feedstock of cyclic hydrocarbons, the feedstock generallycontains between about 2 and 40 mass-% of cyclics comprising naphthenesand aromatics. The aromatics contained in the naphtha feedstock,although generally amounting to less than the alkanes and cycloalkanes,may comprise from 0 to 20 mass-% and more usually from 0 to 10 mass-% ofthe total. Benzene usually comprises the principal aromatics constituentof the preferred feedstock, optionally along with smaller amounts oftoluene and higher-boiling aromatics within the boiling ranges describedabove.

Contacting within the isomerization zones may be effected using thecatalyst in a fixed-bed system, a moving-bed system, a fluidized-bedsystem, or in a batch-type operation. A fixed-bed system is preferred.The reactants may be contacted with the bed of catalyst particles ineither upward, downward, or radial-flow fashion. The reactants may be inthe liquid phase, a mixed liquid-vapor phase, or a vapor phase whencontacted with the catalyst particles, with excellent results beingobtained by application of the present invention to a primarilyliquid-phase operation. The isomerization zone may be in a singlereactor or in two or more separate reactors with suitable meanstherebetween to ensure that the desired isomerization temperature ismaintained at the entrance to each zone. Two or more reactors insequence are preferred to enable improved isomerization through controlof individual reactor temperatures and for partial catalyst replacementwithout a process shutdown.

Isomerization conditions in the isomerization zone include reactortemperatures usually ranging from about 25° C. to 300° C. Lower reactiontemperatures are generally preferred in order to favor equilibriummixtures having the highest concentration of high-octane highly branchedisoalkanes and to minimize cracking of the feed to lighter hydrocarbons.Temperatures in the range of about 100° C. to about 250° C. arepreferred in the process of the present invention. Reactor operatingpressures generally range from about 100 kPa to 10 Mpa absolute,preferably between about 0.3 and 4 Mpa. Liquid hourly space velocitiesrange from about 0.2 to about 25 hr⁻¹, with a range of about 0.5 to 10hr⁻¹ being preferred.

Hydrogen is admixed with or remains with the paraffinic feedstock to theisomerization zone to provide a mole ratio of hydrogen to hydrocarbonfeed of from about 0.01 to 20, preferably from about 0.05 to 5. Thehydrogen may be supplied totally from outside the process orsupplemented by hydrogen recycled to the feed after separation from thereactor effluent. Light hydrocarbons and small amounts of inert materialsuch as nitrogen and argon may be present in the hydrogen. Water shouldbe removed from hydrogen supplied from outside the process, preferablyby an adsorption system as is known in the art. In a preferredembodiment, the hydrogen to hydrocarbon mole ratio in the reactoreffluent is equal to or less than 0.05, generally obviating the need torecycle hydrogen from the reactor effluent to the feed.

Upon contact with the catalyst, at least a portion of the paraffinicfeedstock is converted to desired, higher octane, isoparaffin products.The catalyst of the present invention provides the advantages of highactivity and improved stability.

The isomerization zone generally also contains a separation section,optimally comprising one or more fractional distillation columns havingassociated appurtenances and separating lighter components from anisoparaffin-rich product. Optionally, a fractionator may separate anisoparaffin concentrate from a cyclics concentrate with the latter beingrecycled to a ring-cleavage zone.

Preferably part or all of the isoparaffin-rich product and/or theisoparaffin concentrate are blended into finished gasoline along withother gasoline components from refinery processing including, but notlimited to, one or more of butanes, butenes, pentanes, naphtha,catalytic reformate, isomerate, alkylate, polymer, aromatic extract,heavy aromatics, gasoline from catalytic cracking, hydrocracking,thermal cracking, thermal reforming, steam pyrolysis and coking,oxygenates such as methanol, ethanol, propanol, isopropanol, tert-butylalcohol, sec-butyl alcohol, methyl tertiary butyl ether, ethyl tertiarybutyl ether, methyl tertiary amyl ether and higher alcohols and ethers,and small amounts of additives to promote gasoline stability anduniformity, avoid corrosion and weather problems, maintain a cleanengine and improve driveability.

The following examples serve to illustrate certain specific embodimentsof the present invention. These examples should not, however, beconstrued as limiting the scope of the invention as set forth in theclaims. There are many possible other variations, as those of ordinaryskill in the art will recognize, which are within the scope of theinvention.

EXAMPLE 1

Catalyst samples of Tables 1, 2, and 3 were prepared starting withzirconium hydroxide that had been prepared by precipitating zirconylnitrate with ammonium hydroxide at 65° C. The zirconium hydroxide wasdried at 120° C., ground to 40-60 mesh. Multiple discrete portions ofthe zirconium hydroxide were prepared. Solutions of either ammoniummetatungstate or a metal salt (component 1) were prepared and added tothe portions of zirconium hydroxide. The materials were agitated brieflyand then dried with 80° C. to 100° C. air while rotating. Theimpregnated samples were then dried in a muffle oven at 150° C. for 2hours under air. Solutions of a metal salt (component 2, where component2 is not the same as component 1) were prepared and added to the driedmaterials. The samples were briefly agitated and dried while rotating.The samples were then calcined at 600° C. to 850° C. for 5 hours. Thefinal impregnation solutions of chloroplatinic acid were prepared andadded to the solids. The samples were agitated and dried while rotatingas before. The samples were finally calcined at 525° C. in air for 2hours. In Table 1 below, it can be seen that the catalysts were made atsilicon or phosphorous modifier levels of 0.25 mass-%, 0.5 mass-%, 0.75mass-%, 1 mass-%, and 1.5 mass-%; tungstate levels of 10 mass-%, 15mass-%, 20 mass-%, and 25 mass-%; and calcination temperatures of 600°C., 700° C., and 800° C. The catalysts also contained 0.4 mass-%platinum. Table 1 represents a total of 120 different catalysts thatwere made.

In Table 2 below, it can be seen that the catalysts were made at nominalphosphorus modifier levels of 0.025 mass-%, 0.05 mass-%, and 0.1 mass-%;nominal tungstate levels of 20 mass-%, 22.5 mass-%, 25 mass-%, and 30mass-%; and calcination temperatures of 700° C., 800° C., and 850° C.The catalysts also contained nominally 0.4 mass-% platinum. Table 2represents a total of 28 different catalysts that were made. In Table 3below, it can be seen that the catalysts were made at nominal germaniummodifier levels of 0.5 mass-%, 1 mass-%, and 2.5 mass-%; nominaltungstate levels of 10 mass-%, 15 mass-%, and 20 mass-%; and calcinationtemperatures of 600° C., 700° C., and 800° C. The catalysts alsocontained nominally 0.4 mass-% platinum. Table 3 represents a total of27 different catalysts that were made.

TABLE 1 Si (mass %) 0.25 0.25 0.25 0.25 0.5 0.5 0.5 0.5 0.75 0.75 W(mass %) 10 15 20 25 10 15 20 25 10 15 Calc. Temp ° C. 600 600 600 600600 600 600 600 600 600 Si (mass %) 0.25 0.25 0.25 0.25 0.5 0.5 0.5 0.50.75 0.75 W (mass %) 10 15 20 25 15 25 10 20 10 25 Calc. Temp ° C. 700700 700 700 700 700 700 700 700 700 Si (mass %) 0.25 0.25 0.25 0.25 0.50.5 0.5 0.5 0.75 0.75 W (mass %) 10 15 20 25 15 25 10 20 10 25 Calc.Temp ° C. 800 800 800 800 800 800 800 800 800 800 P (mass %) 0.25 0.250.25 0.25 0.5 0.5 0.5 0.5 0.75 0.75 W (mass %) 10 15 20 25 10 15 20 2510 15 Calc. Temp ° C. 600 600 600 600 600 600 600 600 600 600 P (mass %)0.25 0.25 0.25 0.25 0.5 0.5 0.5 0.5 0.75 0.75 W (mass %) 10 15 20 25 1525 10 20 10 25 Calc. Temp ° C. 700 700 700 700 700 700 700 700 700 700 P(mass %) 0.25 0.25 0.25 0.25 0.5 0.5 0.5 0.5 0.75 0.75 W (mass %) 10 1520 25 15 25 10 20 10 25 Calc. Temp ° C. 800 800 800 800 800 800 800 800800 800 Si (mass %) 0.75 0.75 1 1 1 1 1.5 1.5 1.5 1.5 W (mass %) 20 2510 15 20 25 10 15 20 25 Calc. Temp ° C. 600 600 600 600 600 600 600 600600 600 Si (mass %) 0.75 0.75 1 1 1 1 1.5 1.5 1.5 1.5 W (mass %) 20 1515 20 10 25 15 20 25 10 Calc. Temp ° C. 700 700 700 700 700 700 700 700700 700 Si (mass %) 0.75 0.75 1 1 1 1 1.5 1.5 1.5 1.5 W (mass %) 20 1515 20 10 25 15 20 25 10 Calc. Temp ° C. 800 800 800 800 800 800 800 800800 800 P (mass %) 0.75 0.75 1 1 1 1 1.5 1.5 1.5 1.5 W (mass %) 20 25 1015 20 25 10 15 20 25 Calc. Temp ° C. 600 600 600 600 600 600 600 600 600600 P (mass %) 0.75 0.75 1 1 1 1 1.5 1.5 1.5 1.5 W (mass %) 20 15 15 2010 25 15 20 25 10 Calc. Temp ° C. 700 700 700 700 700 700 700 700 700700 P (mass %) 0.75 0.75 1 1 1 1 1.5 1.5 1.5 1.5 W (mass %) 20 15 15 2010 25 15 20 25 10 Calc. Temp ° C. 800 800 800 800 800 800 800 800 800800

TABLE 2 P (mass %) 0.025 0.05 0.05 0.05 0.1 0.1 0.1 W (mass %) 22.5 2025 30 20 25 30 Calc. Temp ° C. 700 700 700 700 700 700 700 P (mass %)0.025 0.05 0.05 0.05 0.1 0.1 0.1 W (mass %) 22.5 20 25 30 20 25 30 Calc.Temp ° C. 800 800 800 800 800 800 800 P (mass %) 0.025 0.05 0.05 0.050.1 0.1 0.1 0.25 0.25 0.25 1 1 1 W (mass %) 22.5 20 25 30 20 25 30 20 2530 20 25 30 Calc. Temp ° C. 850 850 850 850 850 850 850 850 850 850 850850 850

TABLE 3 Ge 0.5 0.5 0.5 1 1 1 2.5 2.5 2.5 W 10 15 20 10 15 20 10 15 20Calc. Temp ° C. 600 600 600 600 600 600 600 600 600 Ge 0.5 0.5 0.5 1 1 12.5 2.5 2.5 W 10 15 20 10 15 20 10 15 20 Calc. Temp ° C. 700 700 700 700700 700 700 700 700 Ge 0.5 0.5 0.5 1 1 1 2.5 2.5 2.5 W 10 15 20 10 15 2010 15 20 Calc. Temp ° C. 800 8oo 800 800 800 800 800 800 800

The materials shown in Table 2 were analyzed by X-ray powder diffractionto determine the nature of the species present. Some materials wereprepared and analyzed in duplicate, resulting in 48 materials beinganalyzed by X-ray powder diffraction. The X-ray patterns were obtainedusing standard X-ray powder diffraction techniques. The radiation sourcewas a high-intensity X-ray tube operated at 45 kV and 35 ma. Thediffraction pattern from the copper K-alpha radiation was obtained byappropriate computer based techniques. Flat compressed powder sampleswere scanned over a 35° (2θ) range from 12.5° to 47.5° (2θ) using atwo-dimensional X-ray detector. Interplanar spacings (d) in Angstromunits were obtained from the position of the diffraction peaks expressedas 2θ where θ is the Bragg angle as observed from digitized data.Intensities were determined from the integrated area of diffractionpeaks after subtracting background, “I_(o)” being the intensity of thestrongest line or peak, and “I” being the intensity of each of the otherpeaks

As will be understood by those skilled in the art, the determination ofthe parameter 20 is subject to both human and mechanical error, which incombination can impose an uncertainty of about +0.4 on each reportedvalue of 20 and up to +0.5 on reported values for nanocrystallinematerials. This uncertainty is, of course, also manifested in thereported values of the d-spacing, which are calculated from the 0values. This imprecision is general throughout the art and is notsufficient to preclude the differentiation of the present crystallinematerials from each other and from the compositions of the prior art.

In reviewing the X-ray powder diffraction patterns obtained for thematerials of Table 2, all samples showed the presence of zirconiumoxide, forty-one of the materials showed the presence of tungsten oxide,and seven of the materials showed the presence of hydrogen phosphatehydrate in addition to the presence of tungsten oxide. A few patternsshowed aluminum which was due to the sample holder. FIG. 9 shows arepresentative sampling of the X-ray diffraction patterns of thoseforty-one materials showing the presence of tungsten oxide. Pattern 1 ofFIG. 9 corresponds to a material having 0.5 mass-% of a phosphoruscomponent and 30 mass-% tungsten component, Pattern 2 of FIG. 9corresponds to a material having no phosphorus component and 30 mass-%tungsten component, and Pattern 3 of FIG. 9 corresponds to a materialhaving 1 mass-% of a phosphorus component and 30 mass-% tungstencomponent. FIG. 10 shows a representative sampling of the X-raydiffraction patterns of those seven materials showing the presence ofhydrogen phosphate hydrate in addition to the presence of tungstenoxide. Pattern 1 of FIG. 10 corresponds to a material having 0.25 mass-%of a phosphorus component and 20 mass-% tungsten component, Pattern 2 ofFIG. 10 corresponds to a material having 0.25 mass-% phosphoruscomponent and 25 mass-% tungsten component, Pattern 3 of FIG. 10corresponds to a material having 0.1 mass-% of a phosphorus componentand 20 mass-% tungsten component, and Pattern 4 of FIG. 10 correspondsto a material having 1 mass-% of a phosphorus component and 25 mass-%tungsten component. The component levels above are nominal. Noheteropoly anion structures, including Keggin structures, were detectedfor any of the materials analyzed by X-ray powder diffraction.

EXAMPLE 2

The catalysts of Example 1 were prepared as described above inExample 1. Also, reference catalysts were prepared as described inExample 1 but with the addition of the modifier step being omitted fromthe preparation. Approximately 95 mg of each sample was loaded into amulti-unit reactor assay. The catalysts were pretreated in air at 450°C. for 6 hours and reduced at 200° C. in H₂ for 1 hour. n-Heptane, 8mol-%, in hydrogen was then passed over the samples at 120° C., 150° C.,and 180° C., approximately 1 atm, and 0.3, 0.6, and 1.2 hr⁻¹ WHSV (basedon heptane only). The products were analyzed using online gaschromatographs.

To exemplify the data, selected results are shown in FIGS. 1-4 forexperiments at 180° C., 0.6 hr⁻¹ WHSV, and using catalysts comprising10, 20 and 25 mass-% W, and 0.4 mass-% Pt. The identity of the modifier(or first component), the amount of modifier, the amount of tungstencomponent, and the calcination temperature are identified along thex-axis of the plots of FIGS. 1-4. Data where the identity of themodifier is listed as “none”, corresponds to a reference catalystcontaining no modifier. FIG. 1 is a plot of the conversion of heptaneachieved by each of the selected catalysts. All of the catalystsindicate activity, with silicon-modified catalysts showing greaterconversion than the phosphorus-modified catalysts. However, at lowphosphorus levels, activity still trends upward at high levels oftungstate and high calcination temperatures. The optimum tungstateamount appears to be in the range of about 20 to about 25 mass-%. Anumber of the catalysts of the present invention however, exhibitgreater conversion with a calcination at 800° C. than at either 750° C.or 850° C. 850° C. Therefore, a preferred calcination temperature is at800° C. The component levels above are nominal.

FIG. 2 shows the selectivity of the catalysts for C₇ isomerization. Thisplot demonstrates that even though some cracking is occurring,selectivities to C₇ isomerization remain high. FIG. 3 shows theselectivity of the catalysts for C₇ isomerization to produce two of thedesired dimethyl-branched isomers, 2,2-dimethylpentane and2,4-dimethylpentane. Again, the data demonstrates that silicon-modifiedcatalysts show superior results and silicon is therefore a preferredmodifier over phosphorus. FIG. 4 shows the yield of the catalysts for C₇isomerization to produce two desired dimethyl-branched isomers,2,2-dimethylpentane and 2,4-dimethylpentane.

The data discussed above indicates a particular preference for siliconas a modifier over phosphorus. Therefore, FIGS. 5-8 present furtherselected results of the experiment where silicon was the modifier. Oneach of FIGS. 5-8, the amount of tungsten on the catalyst, the amount ofmodifier on the catalyst, the calcination temperature of the catalyst,and the weight hourly space velocity of the run is found on the x-axis.In FIG. 5, the y-axis is the conversion of the n-heptane feed. The plotdemonstrates that conversion increases as the amount of tungstenincreases, but conversion decreases as the weight hourly space velocityincreases. However, with other variables remaining constant, increasingthe amount of modifier from 0.25 mass-% to 1.5 mass-% does not have adramatic effect on the conversion. FIG. 6 demonstrates that theselectivity for C₇ isomerization increases with increasing spacevelocity. However, FIG. 7 shows that the opposite is true whenconsidering the selectivity to two of the desired dimethyl-branchedisomers, 2,2-dimethylpentane and 2,4-dimethylpentane. FIG. 8 shows theyield of two of the desired dimethyl-branched isomers,2,2-dimethylpentane and 2,4-dimethylpentane. In general, the results inFIG. 8 indicate that the yield to the specific dimethylpentane isomers(1) decreases as the space velocity is increased; (2) is highest with acalcination temperature of 800° C.; and (3) is greater at the lowerlevels of modifiers. The component levels above are nominal.

1. A catalyst consisting essentially of a support comprising atungstated oxide or hydroxide of at least one of the elements of GroupIVB (IUPAC 4) of the Periodic Table; a phosphorous component selectedfrom the group consisting of a phosphorous oxide, a phosphoroushydroxide, a phosphorous halide, a phosphorous oxyhalide, a phosphorouscarbonate, a phosphorous nitrate, and a phosphorous sulfate; and atleast one platinum-group metal component selected from the groupconsisting of platinum, palladium, ruthenium, rhodium, iridium, osmiumand mixtures thereof.
 2. The catalyst of claim 1 wherein the phosphorouscomponent comprises from about 0.01 to about 10 mass-%, on an elementalbasis, of the catalyst.
 3. The catalyst of claim 1 wherein theplatinum-group metal component comprises from about 0.01 to 2 mass-%, onan elemental basis, of the catalyst.
 4. The catalyst of claim 1 whereinthe element of Group IVB (IUPAC 4) comprises zirconium.
 5. The catalystof claim 1 wherein the catalyst comprises from about 0.5 to about 25mass-% tungsten on an elemental basis.
 6. The catalyst of claim 1wherein the platinum group-metal component consists essentially of onesingle metal selected from the platinum-group metal.
 7. The catalyst ofclaim 1 wherein the second platinum-group metal component is platinum.8. A catalyst consisting essentially of a support comprising atungstated oxide or hydroxide of at least one of the elements of GroupIVB (IUPAC 4) of the Periodic Table; a phosphorous component selectedfrom the group consisting of a phosphorous oxide, a phosphoroushydroxide, a phosphorous halide, a phosphorous oxyhalide, a phosphorouscarbonate, a phosphorous nitrate, and a phosphorous sulfate; at leastone platinum-group metal component selected from the group consisting ofplatinum, palladium, ruthenium, rhodium, iridium, osmium and mixturesthereof; and from about 0.1 to 50 mass-% of a refractory inorganic-oxidebinder.
 9. The catalyst of claim 8 wherein the refractoryinorganic-oxide binder comprises an alumina.
 10. A catalyst consistingessentially of a support comprising a tungstated oxide or hydroxide ofat least one of the elements of Group IVB (IUPAC 4) of the PeriodicTable; a phosphorous component selected from the group consisting of aphosphorous oxide, a phosphorous hydroxide, a phosphorous halide, aphosphorous oxyhalide, a phosphorous carbonate, a phosphorous nitrate,and a phosphorous sulfate; at least one platinum-group metal componentselected from the group consisting of platinum, palladium, ruthenium,rhodium, iridium, osmium and mixtures thereof; and an additionalcomponent selected from the group consisting of at least one Group IVA(IUPAC 14) component, iron, nickel, rhenium, and mixtures thereof. 11.The catalyst of claim 10 wherein the additional component is iron in anamount from about 0.1 to about 5 mass-%.